Overview Heat pump control



This function block applies external requirements to a heat pump: the blocking command of the grid operator, the PV surplus and the temperatures the system wants. The heat pump regulates itself internally - compressor, defrosting and expansion valve are not part of this block. It supplies only enables and setpoints.

The enables go to the heat pump as four operating states over two contacts. The setpoints for heating and hot water are raised when there is surplus, so that the heat pump stores the surplus energy as heat. Without surplus and without a block the block stays inconspicuous: it reports normal operation and passes the base values through unchanged.

If you do not measure the surplus yourself, take it from the Block Energy Manager and connect it to input UE. A measured surplus value can also be connected directly.

The four states

State When Effect
1 Block SB not 0 or mode 2 Contacts as set in Contacts block. The heat pump stays off. The block takes precedence over any surplus, even over mode 3.
2 Normal operation Basic state SH = base value heating, SS = base value hot water.
3 Switch-on recommendation Surplus above the recommendation threshold for the minimum duration (or preload) Both setpoints raised by the recommendation raise.
4 Start command Surplus above the start threshold for the minimum duration, or mode 3 Both setpoints raised by the higher start command raise. The daily budget applies.

Minimum run time and minimum pause lie between the states: a surplus that fluctuates every minute must not switch the heat pump every minute. Recommendation and start command last at least the minimum run time; after leaving them, normal operation lasts at least the minimum pause. Block, fault, buffer limit, daily budget and the end of the preload take effect immediately.

Contact assignment. The standard says: block = contact 1 closed, normal operation = both open, recommendation = contact 2 closed, start command = both closed. That is the default. Some devices assign the contacts differently or inverted - so the assignment per state is adjustable, and both contacts can be inverted. Check this before commissioning: a wrongly assigned contact means, in the worst case, a start command instead of a block.

Setpoints. The base value is input SO or SW; without a value the parameter Base value applies. If a consumer requests more than the base value heating through AN/AT, its temperature applies. The raise of the current state is added. The result is limited to the maximum setpoint - a raise beyond the design value of the system would make the heat pump run into a fault.

Daily budget. The start command may last only a limited time per day. Without this budget the building would be overheated in summer with a lot of surplus. Once it is used up, the state falls back to recommendation or normal operation. Mode 3 is a manual decision and overrides the budget, but not the block and not the buffer limit. The budget survives a restart of the controller and starts again with every new day.

Preload before a block. If the blocking times of the grid operator are known, the block can raise the buffer beforehand so that the building bridges the block. The block has no schedule of its own because blocking times differ by region and change: the time window before the block comes from a schedule (Block Time switch) and is connected to input VF. The preload is off by default. It works only if the parameter Preload is on and VF is present - without known blocking times it has no effect. During the preload the switch-on recommendation applies, the heating setpoint is raised by the raise buffer, and output VL is 1. With a connected buffer sensor it ends as soon as the buffer has reached the raised setpoint.

Buffer limit. When the buffer reaches the buffer maximum temperature, the block returns to normal operation immediately (back at 2 K below). This protects against permanent overheating.

Example

Brine heat pump with a 1000 litre buffer, PV system and a grid block from 11 to 13 o'clock. The surplus comes from the Energy Manager at UE. A schedule puts the blocking times on SB; a second switching time one hour before is on VF. Parameters: recommendation from 1000 W, start command from 2500 W, preload on, buffer maximum temperature 60 °C. Result: at 10 o'clock the system preloads the buffer, from 11 to 13 the heat pump stays off, and in the sunny afternoon it runs on recommendation or start command and stores the surplus in the buffer.

Inputs

UE Surplus in watts Optional. A value at or above the recommendation or start threshold switches to state 3 or 4 once it has been present for the minimum duration. Whether a positive or a negative value is surplus is set by the parameter Surplus is. Not connected: there is never surplus, the block stays in normal operation.
SB Block command grid operator Optional. Not 0 blocks (state 1), 0 releases. Applies as long as the value is present. Not connected: never blocked.
AN Heat request Optional. Bit of the heat request of a consumer (heating circuit, hot water, collector). Not 0 counts as a request whose temperature AT may then exceed the base value heating. Not connected: only AT counts - a temperature above 0 counts as a request.
AT Heat request temperature Optional. Temperature wanted by the consumer. Acts only while a request is present: if it is higher than the base value heating, it becomes the base value. Not connected: the base value stays unchanged.
TP Buffer temperature Optional. Basis of the buffer limit and of the end of the preload. Not connected: no buffer limit, the preload runs as long as VF is present.
SO Setpoint heating (base value) Optional. Not connected or 0: the parameter Base value heating applies.
SW Setpoint hot water (base value) Optional. Not connected or 0: the parameter Base value hot water applies.
BA Mode Optional. 0 automatic, 1 normal operation only (no surplus), 2 blocked, 3 force start command. An unknown value counts as automatic. Not connected: automatic.
SM Fault signal heat pump Optional. Not 0 reports a fault; it counts only once it has been present longer than the fault signal delay. Then SR is 1 and the block goes to normal operation. Not connected: a fault is never detected.
FR Enable Optional. 0 takes away the surplus use of the block: it stays in normal operation. The block of the grid operator still applies. Not 0 enables. Not connected: the block counts as enabled. Use this input if another consumer is to have priority.
VF Preload enable Optional. Not 0 reports the time window before a block. Acts only if the parameter Preload is on. Not connected: no preload.

Outputs
K1 Contact 1 Contact 1 of the enable interface, according to state and parameters.
K2 Contact 2 Contact 2 of the enable interface, according to state and parameters.
ZU State 1 block, 2 normal operation, 3 recommendation, 4 start command.
SH Setpoint heating Base value, raised and limited if applicable. To the device or to the Modbus master.
SS Setpoint hot water Base value, raised and limited if applicable. To the device or to the Modbus master.
VL Preload running 1 during the preload.
GS Blocked 1 in the block state.
ST Status text State in plain text (in German, ASCII, written by the runtime). For a text address.
SR Fault 1 with a fault signal of the heat pump and with a block that lasts longer than the block maximum duration.
BT Operating hours surplus use Hours in the states recommendation and start command. Survives a restart of the controller.

Parameters
Contacts block / normal operation / recommendation / start command Which contacts are closed in the state. Default according to the standard: block contact 1, normal operation open, recommendation contact 2, start command both.
Invert contact 1 / 2 Inverts the output, for devices with a normally closed contact. Default off.
Surplus is Positive or negative (grid power measurement, feed-in negative). Default positive.
Surplus hysteresis A state is left only when the surplus falls below its threshold by this value. Default 200 W.
Recommendation: threshold, minimum duration, raise heating/hot water Default 1000 W, 5 min, 3 K and 3 K. Threshold 0 switches the recommendation off.
Start command: threshold, minimum duration, raise heating/hot water, daily budget Default 2500 W, 5 min, 5 K, 7 K and 240 min. Threshold 0 switches the start command off, budget 0 = unlimited.
Block maximum duration, block on exceeding If the block of the grid operator lasts longer, SR reports a fault. "Report only" keeps the block, "End block" lifts it - the block then works on the surplus again. Default 0 = unlimited, report only. A block through the mode is never limited.
Preload, raise buffer Default off, 5 K.
Minimum run time per state, minimum pause Default 10 min and 5 min.
Base value heating / hot water Apply as long as SO or SW are not connected. Default 35 °C and 48 °C.
Maximum setpoint heating / hot water Limits the setpoint including the raise. Default 60 °C. 0 = no limit.
Buffer maximum temperature Default 60 °C. 0 = no limit. Acts only with input TP connected.
Fault signal delay Default 60 s.

See also general parameters of all function blocks.